1. Field of the Invention
The present invention relates to a seat, particularly a vehicle seat mounted in a vehicle such as an automobile.
2. Description of the Related Art
Vehicle seats are configured so that, for example, a back portion (i.e., seatback) is connected to a rear end portion of the seat portion (i.e., seat cushion) so that the tilting positions are adjustable through a reclining mechanism.
A configuration provided with a thick-type back portion frame for ensuring the rigidity of the back portion is known. Since the rigidity of the back portion frame is high with this type of vehicle seat, shock absorption by frame deformation during collision is not achieved and the force of the shock (i.e., acceleration) is conveyed to the person seated in the chair as is with no reduction, and there are concerns that it might impart damage to the seat occupant. Further, since the rigidity of the back portion frame is high with this type of vehicle seat, vibration absorption depends on the cushion material provided at the back portion frame and forming the backrest, so it has been difficult to obtain favorable vibration absorption qualities.
On the other hand, a vehicle seat provided with a thin highly elastic back portion frame has also been developed. With this type of vehicle seat, sufficient rigidity of the back portion is ensured during normal driving. Nevertheless, with this type of vehicle seat, when large impact force acts upon it directly, as, for example, is the case when the front portion of the vehicle collides into something (front collision) and cargo or freight loaded in the luggage compartment or the rear seat collides into the back portion, the rigidity is insufficient. When plastic deformation of the back portion frame occurs, it is thought possible that it will tilt forward greatly relative to the seat portion. When plastic deformation of the back portion frame occurs, the survival space of the seat occupant reduces while the shock that accompanies rocking return towards the back of the person cannot be absorbed (i.e., the shock-absorbing stroke is insufficient). Further, with this kind of vehicle seat, there is insufficient rigidity relative to shock so, for example, at the time of rear collision, there are cases where movement towards the rear relative to the seat of the seat occupant (especially in the pelvis region) cannot be effectively deterred.
Furthermore, vehicle seats are known that are provided, at the base end side of the back portion frame, with a reinforcing component that follows along the widthwise direction of the vehicle (see, for example, the Official Gazette of Japanese Patent Application Laid-Open (JP-A) No. 6-1174). With this vehicle seat, the survival space of the seated person in the widthwise direction of the vehicle is ensured at the time of side collision due to the reinforcing component. Nonetheless, with this vehicle seat, the reinforcing component simply made highly rigid and being free at both ends cannot itself absorb impact so this is only absorbed by the relative movement of the entire seat to the vehicle and by the conveying of shock to the floor of the vehicle and the like. Further, for this reason the arrangement of the reinforcing component is also limited to the lower part of the back portion, so safety against collision from, as described above, freight and the like during a frontal collision cannot be achieved.